This invention relates to fuel metering and injection systems for internal combustion engines incorporating means for providing the injectors with a supply of fuel at a high, regulated pressure. The invention may be used in a fuel injection system, such as that described in my U.S. patent application Ser. No. 629,421, entitled "Fuel Injection System," filed concurrently herewith on Nov. 6, 1975. The invention is related to my U.S. Pat. No. 3,507,263 issued Apr. 21, 1970.
In fluid metering and injection systems employing electrically actuated injectors, the precision of control of the injection volume is proportional to both the magnitude of the fluid pressure in the conduit feeding the injectors. The degree of regulation of the pressure to a high, regulated pressure is desirable. With relatively large engines, the injection systems may also be called up to produce high flow rates of fuel. Previous systems typically employed electric pumps powered by the vehicle electric system to provide this large fuel volume at pressure to the injectors. These pumps may produce a flow in excess of the maximum fuel demands of the engine and the excess fuel was fed back to the fuel tank through a pressure overflow valve and a return conduit. At low throttle levels a large portion of the pumped fuel was returned and, as a result, the gasoline might be circulated through the pump a large number of times before finally being admitted to a combustion cylinder. The resulting churning and agitation of the gas is generally considered deleterious to its combustion characteristics.
High pressure, high volume fluid pumps have been generally unavailable. Attempts to achieve such a design have produced pumps which are expensive, unreliable, large and noisy. In the prior art, the conflict between cost and performance was typically simplified by lowering the pressure of the system to a compromise level of pressure. Previous fuel injection systems typically employed fuel pressures of about 25-40 psig. in the fuel lines to the injectors while pressures in excess of twice these values would be desirable for increasing the precision of the injection process.
Previous fuel injection systems have required regulation of the pressure of the fuel provided to the injectors. Since the fuel flow through the injector is a function of the fuel line pressure, variations in that pressure result in variations in volume of fuel injected into a cylinder. The primary purpose of the fuel injection system is to improve the control of the volume of fuel fed to each cylinder over the relatively rough control obtained with conventional carburetion systems. Large variations in the fuel pressure to the injectors defeat the central purpose of the fuel injection system. In previous systems, the pressure regulation was adversely affected by line pressure drops which occurred each time an injector was actuated and instantaneously reduced the fuel pressure at the injector. This produced a low pressure, or expansion wave, which traveled through the system, reducing the localized fuel pressure at its locus. These pressure waves would be reflected from the end walls of the system. The rapid actuation of the injectors would induce a number of these waves, resulting in variations in the fuel pressure throughout the lines feeding the injectors.
The present invention is broadly directed toward a fuel injection system capable of providing substantially higher fuel pressures in the fuel lines to the injectors than systems of the prior art and of attaining a much higher degree of regulation of that pressure so that the quantity of fuel fed to a cylinder intake valve upon actuation of the injector is substantially a function of the time duration during which the injector is actuated.